The present invention relates generally to contamination detection systems for determining contamination levels in fluid samples and, more particularly, to such a system used in the testing of fuel samples to determine the particulate and free water levels in the fuel supply from which the sample is taken, thereby ensuring the delivery and use of clean, dry fuel.
A variety of particulate detection systems are currently used in laboratories and in field operations to determine contaminant levels in various fluid testing applications. For example, an important application for a contamination detection system is the testing of aircraft fuel supplies for unacceptable levels of particulate and free water contamination. Typically, two fuel samples are tested by a particulate detector and a free water detector, respectively, in accordance with a variety of testing methods.
Particulate detectors currently in use are based upon one of several conventional techniques utilizing a membrane filter on which particulates are deposited. The membrane filter is analyzed to determine the amount of particulates on the filter, thereby indicating the concentration of particulates in the fluid sample. The most common methods currently used to analyze the membrane filter are Gravimetric Assessment, Colormetric Assessment, or Visual Assessment.
The Gravimetric Assessment method of analyzing the membrane filter involves actual weighing of the particulate products retained on the membrane filter after the fluid has been passed therethrough. The Colormetric Assessment method involves evaluating the particulate laden membrane filter on the basis of coIoration, hue, chroma, and intensity. The Visual Assessment method relies upon a skilled operator to correctly identify the quality and quantity of particulates deposited on the membrane filter.
As previously noted, particulate detection systems are used in the field testing of aircraft fuel supplies. One such fuel testing system is disclosed in U.S. Pat. No. 4,044,604, assigned to the assignee of the present invention, which utilizes the principle of differential light transmission through membrane filters to measure particulate contamination levels More specifically, a fuel sample is passed through a pair of membrane filters, wherein the first filter traps particulates and acquires fuel coloration while the second filter acquires only fuel coloration. Individual opacity readings are taken of the respective filters as they are successively placed in a single filter holder, and then a differential reading is manually calculated, whereby the differential reading represents a measure of particulate level independent of fuel coloration.
In each of the aforementioned methods of analyzing a membrane filter to determine the particulate count, the accuracy of the measurement is affected by excessive handling of the sample filter, resulting in filter contamination and measurement errors. Also, the prior art sample filter handling methods are cumbersome and necessitate long cycle times for conducting contamination tests.
The present invention is directed to overcoming the aforementioned problems associated with prior art contamination detection systems, wherein it is desired to provide an improved membrane filter handling apparatus that improves the accuracy of contamination test results, and minimizes the cycle time required to perform the tests. It is further desired to provide a fuel contamination detection system that combines a particulate detector and free water detector in an inexpensive, compact package.